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Disks acting a very slowly through the fibre channel on HP-UX 11i v3

 
tahors
Occasional Visitor

Disks acting a very slowly through the fibre channel on HP-UX 11i v3

Hello

 

When we doing a simple test like "timex dd if=/dev/zero ..." we gets speed ~130MBps. But having the same equipment (other blades) on Linux we can get 500~600MBps. Please help us find out where is the bottleneck.

Some info here:

HP 451871-B21 8Gb Dual Port PCIe Fibre Channel Mezzanine

HP-UX testmach B.11.31 U ia64

Driver Version = @(#) fcd B.11.31.1109 May 23 2011

patchinfo? other information?

5 REPLIES
Torsten.
Acclaimed Contributor

Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3

What kind of device is the target and check if you use by chance the "standby" path?


Hope this helps!
Regards
Torsten.

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Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3

As Torsten said, you need to tell us what sort of disk array you are talking to here.. there are many variables that could make a significant difference to why Linux appears faster - top of my list for something as straightforward as a sequential IO operation like a dd would be

 

i) block sizes (influenced by the filesystem - although you don't indicate whether you were doing the dd to a filesystem, to the block device, or to the raw device?)

ii) disk SCSI queue depths - I don't know what the default is on Linux, but it may be deeper than the default of 8 on HP-UX - this is a farirly in-depth topic - see this whitepaper for details: http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c02054623/c02054623.pdf

iii) MPIO settings - the default of round-robin on HP-UX is not great for sequential IO with many disk arrays - again you'd have to tell me what Linux is set to for comparison... for example on XP disk arrays for sequential IO, I have often found weighted_rr with a wrr_path_weight of about 1000 per LUNpath works much better


HTH

Duncan
tahors
Occasional Visitor

Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3

On other side of fibre channel we have SAN switch connected to 3PAR disk array.

i) i have mounted test block device 10G with vxfs file system to perform dd

The full string look like to

timex dd if=/dev/zero of=/test_ssd/file count=8192k bs=1024

 

ii) depth is really 8 there (we didn't change standart value). I will change and test. Thanks

iii) Usally to avoid multipath influence i gave only one path from 3par storage.

 

PS: After deleting stale devices from system the speed slumped to 40MBps.

Torsten.
Acclaimed Contributor

Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3

bs could be larger.

The server has 8Gb, the array port probably only 4Gb. Using multipath would be better - check also if the host mode is set to hpux on the array.

 

Consider a bad connection/cable also.


Hope this helps!
Regards
Torsten.

__________________________________________________
There are only 10 types of people in the world -
those who understand binary, and those who don't.

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Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3

iii) Usally to avoid multipath influence i gave only one path from 3par storage

 

You may still be doing multi-pathing... by default if you use a legacy DSF on HP-UX11.31 (i.e. /dev/rdsk rather than /dev/rdisk), you will still be doing multi-pathing... see the attribute leg_mpath_enable in the scsimgr(1m) man page


HTH

Duncan